utimens: work around older Linux failure with symlinks

Some Linux kernel versions support utimensat(,0) but not
utimensat(,AT_SYMLINK_NOFOLLOW), even for non-symlinks.  Had the
fallback code for regular files been reached, it would have truncated
timestamps.  But since glibc lutimes just wraps utimensat, and we
didn't expect ENOSYS from lutimes, the fallback wasn't even reached.

* lib/utimens.c (lutimensat_works_really): New variable.
(fdutimens, lutimens): Use it to manage kernels that support
nanosecond times on files, but not on symlinks.
Reported by Ondřej Vašík.

Signed-off-by: Eric Blake <ebb9@byu.net>

1 files changed, 16 insertions, 8 deletions

diff --git a/lib/utimens.c b/lib/utimens.c
index eb63487c43..9e66ffca6f 100644
--- a/lib/utimens.c
+++ b/lib/utimens.c
@@ -54,10 +54,12 @@ struct utimbuf
 #undef utimensat
 
 #if HAVE_UTIMENSAT || HAVE_FUTIMENS
-/* Cache variable for whether syscall works; used to avoid calling the
-   syscall if we know it will just fail with ENOSYS.  0 = unknown, 1 =
-   yes, -1 = no.  */
+/* Cache variables for whether the utimensat syscall works; used to
+   avoid calling the syscall if we know it will just fail with ENOSYS.
+   There are some Linux kernel versions where a flag of 0 passes, but
+   not AT_SYMLINK_NOFOLLOW.  0 = unknown, 1 = yes, -1 = no.  */
 static int utimensat_works_really;
+static int lutimensat_works_really;
 #endif /* HAVE_UTIMENSAT || HAVE_UTIMENSAT */
 
 /* Solaris 9 mistakenly succeeds when given a non-directory with a
@@ -242,6 +244,7 @@ fdutimens (char const *file, int fd, struct timespec const timespec[2])
 # endif /* HAVE_FUTIMENS */
     }
   utimensat_works_really = -1;
+  lutimensat_works_really = -1;
 #endif /* HAVE_UTIMENSAT || HAVE_FUTIMENS */
 
   /* The platform lacks an interface to set file timestamps with
@@ -381,7 +384,7 @@ lutimens (char const *file, struct timespec const timespec[2])
      worry about bogus return values.  */
 
 #if HAVE_UTIMENSAT
-  if (0 <= utimensat_works_really)
+  if (0 <= lutimensat_works_really)
     {
       int result = utimensat (AT_FDCWD, file, ts, AT_SYMLINK_NOFOLLOW);
 # ifdef __linux__
@@ -398,10 +401,11 @@ lutimens (char const *file, struct timespec const timespec[2])
       if (result == 0 || errno != ENOSYS)
         {
           utimensat_works_really = 1;
+          lutimensat_works_really = 1;
           return result;
         }
     }
-  utimensat_works_really = -1;
+  lutimensat_works_really = -1;
 #endif /* HAVE_UTIMENSAT */
 
   /* The platform lacks an interface to set file timestamps with
@@ -416,7 +420,9 @@ lutimens (char const *file, struct timespec const timespec[2])
         return 0;
     }
 
-#if HAVE_LUTIMES
+  /* On Linux, lutimes is a thin wrapper around utimensat, so there is
+     no point trying lutimes if utimensat failed with ENOSYS.  */
+#if HAVE_LUTIMES && !HAVE_UTIMENSAT
   {
     struct timeval timeval[2];
     struct timeval const *t;
@@ -431,9 +437,11 @@ lutimens (char const *file, struct timespec const timespec[2])
     else
       t = NULL;
 
-    return lutimes (file, t);
+    result = lutimes (file, t);
+    if (result == 0 || errno != ENOSYS)
+      return result;
   }
-#endif /* HAVE_LUTIMES */
+#endif /* HAVE_LUTIMES && !HAVE_UTIMENSAT */
 
   /* Out of luck for symlinks, but we still handle regular files.  */
   if (!(adjustment_needed || REPLACE_FUNC_STAT_FILE) && lstat (file, &st))